1. Field of the Invention
The present invention relates to a thin film magnetic head and a method of manufacturing the same, and more particularly relates to a combination type thin film magnetic head having an inductive type writing thin film magnetic head element having a thin film coil and a magnetoresistive type reading thin film magnetic head element stacked one on the other, and a method of manufacturing the same. More particularly, the present invention relates to a combination type thin film magnetic head and a method of manufacturing the same, in which a GMR element is used as a magnetoresistive type thin film magnetic head element and an inductive type thin film magnetic head element has a superior NTSL property by extremely shortening a magnetic path length by reducing a coil winding pitch of a thin film coil and has a narrow record track for attaining a high surface recording density on a magnetic record medium by providing a miniaturized track pole made of a magnetic material having a high saturation magnetic flux density.
2. Description of the Related Art
Recently a surface recording density of a hard disc device has been improved, and it has been required to develop a thin film magnetic head having an improved performance accordingly. A recent magnetoresistive type thin film magnetic head using a GMR (Giant Magneto-Resistive) element has a surface recording density up to 100-200 gigabits/platter. A combination type thin film magnetic head is constructed by stacking, one a substrate, an inductive type thin film magnetic head element intended for writing information on a magnetic record medium and a magnetoresistive type thin film magnetic head element intended for reading information out of the magnetic record medium. As a reading magnetoresistive element, a GMR element having a magnetoresistive change larger than a normal anisotropic MR element by more than 20 times has been used. In order to improve a performance of the GMR element, there have been various proposals.
In a normal anisotropic MR element, a single film of a magnetic material showing the magnetoresistive effect is utilized. Many GMR elements have a multi-layer structure having a stack of a plurality of films. The GMR element has a simple structure and has a larger resistance change under a weak magnetic field. A spin-valve GMR film will be suitable for a large scale manufacture. A performance of the reading head element is determined by not only the above mentioned selection of materials, but also by pattern widths such as an MR height and a track width. The track width is determined by a photolithography process and the MR height is determined by an amount of polishing for forming an air bearing surface (ABS).
At the same time, the performance of the recording magnetic head is also required to be improved in accordance with the improvement of the performance of the reproducing magnetic head. In order to increase a surface recording density, it is necessary to realize a high track density on a magnetic record medium. To this end, a pole portion of the recording thin film magnetic head element has to be narrowed in a sub-micron order, particularly not larger than 0.2 μm by utilizing the semiconductor manufacturing process. However, upon decreasing a track width by utilizing the semiconductor manufacturing process, there is a problem that a sufficiently large magnetic flux could not be obtained due to a miniaturized structure of the pole portion. In this manner, by replacing the MR film by the GMR film in the reproducing head element and by selecting a material having a high magnetoresistive sensitivity, it is possible simply to attain a desired high surface recording density.
In order to realize a sufficiently high surface recording density of about 100-200 gigabits/platter, it is necessary to use a record medium, i.e. a magnetic disk material having a high magnetic coercive force. If a magnetic material having a high coercive force is not used, once recorded data might be erased due to the thermal fluctuation. When a material magnetic having a high coercive force is used, recoding requires a large magnetic flux, and therefore an inductive type thin film magnetic head element must generate a large magnetic flux. Generally, in order to generate a large magnetic flux in the inductive type thin film magnetic head element, a track pole is made of a magnetic material having a high saturation magnetic flux density (Hi-Bs material having a saturation magnetic flux density not less than 1.8 T (tesla). NiFe (80:20) of 1.0 T and NiFe (45:55) of 1.5 T have been used as a magnetic material having a high saturation magnetic flux density. Recently, CoNiFe of 1.8˜2.1 T has been used. In order to use a miniaturized track pole stably, a magnetic material having saturation magnetic flux density not less than 2.0 T is generally used. However, when a width of the track pole is reduced to sub-micron order, such magnetic materials could not generate a sufficiently large magnetic flux for recording stably. In this manner, it is required to use a magnetic material having a much higher saturation magnetic flux density. Heretofore, when a track pole is made of a magnetic material having a high saturation magnetic flux density, a plating method has been generally used. However, in order to manufacture a track pole having a narrow width, it is preferable to use a sputtering method. From this view point, it will be advantageous to form a track pole by sputtered films of FeN having a saturation magnetic flux density of 2.0 T or FeCo and CoFeN having a saturation magnetic flux density of about 2.4 T.
FIGS. 1-9 are cross sectional views showing successive steps of a method of manufacturing a conventional combination type thin film magnetic head having a GMR element. In these drawings, A represents a cross sectional view cut along a plane perpendicular to the air bearing surface and B denotes a cross sectional view of a pole portion cut along a plane parallel to the air bearing surface. The combination type thin film magnetic head includes an inductive type recording magnetic head element provided on a magnetoresistive type reading magnetic head element.
As shown in FIGS. 1A and 1B, an alumina (Al2O3) insulating film 2 having a thickness of about 2-3 μm is deposited on a substance 1 made of AlTiC. Next, a bottom shield film 3 made of a magnetic material for magnetically shielding a GMR reading head element from an external magnetic field is formed on the alumina insulating film. On the bottom shield film 3, a bottom shield gap film 4 made of alumina is formed with a thickness of 30-35 nm by sputtering. Then, a GMR film 5 having a given layer-structure is formed, and lead electrodes 6 for the GMR film are formed by a lift-off process. Next, a top shield gap film 7 made of alumina is formed with a thickness of 30-35 nm by sputtering, and a magnetic material film 8 serving as a top magnetic shield film is formed with a thickness of about 3 μm.
Next, an isolation film 9 made of alumina is formed with a thickness of about 0.3 μm for isolating the reading GMR head element from a writing induction type thin film magnetic head element to suppress noise in a reproduced output from the GMR head element. After that, a bottom pole 10 of the recording head element is formed with a thickness of 1.5-2.0 μm. The bottom pole 10 is formed by a plating film of CoNiFe. It should be noted that in the drawings a ratio of thickness of various portions does not exactly correspond to an actual ratio. For instance, the isolation film 9 is shown to have a smaller thickness.
Next, as depicted in FIGS. 2A and 2B, on the bottom pole 10, is formed a write gap film 11 made of a non-magnetic material to have a thickness of about 100 nm, and a top track pole 12 made of a permalloy which is a magnetic material having a high saturation magnetic flux density is formed in accordance with a given pattern. At the same time, a bridge portion 13 for magnetically coupling the bottom pole 10 with a top pole to be formed later at a back-gap is formed. The top track pole 12 and bridge portion 13 are formed by plating with a thickness of about 3-4 μm.
Then, in order to avoid a widening of an effective track width, i.e. in order to prevent a magnetic flux from extending at the bottom pole 10 during a writing operation, the write gap film 11 and the underlying bottom pole 10 around the top track pole 12 are etched by ion milling to form a so-called trim structure. After forming an alumina insulating film 14 having a thickness of about 3 μm over a whole surface, a surface is flattened by the chemical mechanical polishing (CMP) as shown in FIGS. 3A and 3B.
Next, as illustrated in FIGS. 4A and 4B, in order to form a thin film coil by the electrolytic plating of Cu, a thin seed layer 15 of Cu is formed by sputtering with a thickness of about 100 nm. After forming a resist film having a given opening pattern on the seed layer, a first layer thin film coil 16 is formed with a thickness of 1.5 μm in accordance with a given pattern by a plating process using a copper sulfate liquid. Then, after removing the resist film, the exposed seed layer 15 is removed by an ion milling process using an argon ion beam as depicted in FIGS. 5A and 5B. In this manner, the seed layer 15 is removed to separate adjacent coil windings to form a coiled conductor. During the ion milling, in order to prevent portions of the seed layer 15 projecting from side edges of the coil windings of the thin film coil 16 from being remained, the ion milling is performed at an angle of 5-10°. When the ion milling is carried out at an angle near a perpendicular angle, debris of the seed layer 15 splashed by impingement of the ion beam might be adhered again to the coil windings. Therefore, a distance between successive coil windings must be widened.
Then, as shown in FIGS. 6A and 6B, an insulating film 17 which supports the first layer thin film coil 16 in an electrically insolated manner is formed by photoresist. Next, as depicted in FIGS. 7A and 7B, a Cu seed layer 18 is formed and a second layer thin film coil 19 is formed in accordance with a given pattern with a thickness of 1.5 μm. Then, after removing the seed layer 18 by ion milling, an insulating film 20 of photoresist for supporting the second layer thin film coil 19 in an electrically insulating manner is formed. Next, as illustrated in FIGS. 8A and 8B, a top pole 21 made of permalloy is formed with a thickness of about 3 μm such that the top track pole 12 and bridge portion 13 are coupled with each other by the top pole 21, and a whole surface is covered with an overcoat film 22 made of alumina. It should be noted that during the formation of the second layer thin film coil 19, a connect portion 23 for connecting inner portions of the first and second layer thin film coils 16 and 19 is formed. Finally, an end surface into which the GMR film 5, write gap film 11, top track pole 12 and so on are exposed is polished to form an air bearing surface ABS to complete a slider. In a manufacturing process for forming an actual thin film magnetic head, after forming a number of the above mentioned structures on the wafer, the wafer is divided in a plurality of bars in each of which a number of thin film heads are aligned. Then, a side edge of the bar is polished to obtain the air bearing surface ABS.
FIG. 9 shows schematically a cross sectional view and a plan view illustrating the structure of the known combination type thin film magnetic head manufactured in the manner explained above. The bottom pole 10 has a large area, but the top track pole 12 and top pole 21 have a smaller area than the bottom pole. One of factors determining the performance of the writing head element is a throat height TH. The throat height TH is a distance from the air bearing surface ABS to an edge of the insulating film 14, and this distance is desired to be short. One of factors determining the performance of the reading head element is an MR height MRH. This MR height (MRH) is a distance from the air bearing surface ABS into which one edge of the GMR film 15 is exposed to the other edge of the GMR film. During the manufacturing process, a desired MR height MRH is obtained by controlling an amount of polishing the air bearing surface ABS.
Now problems in the known combination type thin film magnetic head mentioned above will be explained. After forming the insulating film 17, 20 such that the thin film coil 16, 19 is supported by the insulating film in an electrically insulating manner, the top pole 21 is formed. In this case, the top pole 21 has to be formed into a given pattern along the side wall of the insulating film 17, 20. To this end, a photoresist is formed with a thickness of 3-4 μm at a step of the insulating film having a height of about 7-10 μm.
Now it is assumed that at the side wall of the insulating film 16, 19, the photoresist should have a thickness of at least 3 μm, a thickness of the photoresist at the bottom of the step would become thick such as 8-10 μm. Since a width of record track of the writing head is mainly determined by a width of the top track pole 12, it is not necessary to miniaturize the top pole 21 compared with the top track pole 12, but if the track width of submicron order such as 0.2 μm is desired, the pole portion of the top pole 21 should be miniaturized in the order of submicrons.
Upon forming the top pole 21 into a desired pattern by plating, the photoresist has to be deposited on the top track pole 12 and insulating film 17, 20 having the step of more than 10 μm such that the photoresist has a uniform thickness. Then, the photoresist is subjected to the exposure of light to form the top pole 21 having the pole portion of submicron order. That is to say, a pattern of submicron order must be formed with the photoresist having a thickness of 8-10 μm. When the pole portion 21 is formed by plating, a seed layer made of permalloy serving as an electrode is previously formed. During the light exposure of the photolithography, light is reflected by the permalloy seed layer, and a desired pattern might be deformed. Therefore, it is quite difficult to form the pattern of submicron order precisely.
In order to improve the surface recording density, it is required to miniaturize the pole portion as explained above. Then, the miniaturized pole portion must be made of a magnetic material having a high saturation magnetic flux density. In general, FeN and FeCo have been known as magnetic materials having a high saturation magnetic flux density. However, these magnetic materials could not be easily formed by sputtering into a film having a given pattern. It has been known to shape the sputtered film into a given patter by the ion milling. However, etching rate is too slow and a track width of submicron order could not be controlled precisely. Moreover, by reducing a size of the pole portion, the bottom track pole must be also miniaturized, and therefore a volume of the bottom track pole would be decreased. Then, undesired saturation of magnetic flux is liable to occur.
NiFe of 1.5 T, CoNiFe of 1.9-2.1 T, FeCo of 2.1-2.3 T have been known as magnetic materials having a high saturation magnetic flux density, and these magnetic materials could be relatively easily formed into a given pattern by plating. For instance, Fe rich NiFe (more than 50%) has a saturation magnetic flux density of 1.5-1.6 T, and a composition could be controlled stably. However, in order to realize a surface recording density of 100-200 gigabits/platter, a track width has to be not larger than 0.2 μm. Then, there would be required to use a magnetic material having a higher saturation magnetic flux density. There has been proposed to form a magnetic film by plating using CoFe and CoNiFe having higher magnetic flux density than NiFe. However, these magnetic materials could provide the magnetic faculty of about 1.8-2.1 T. In order to realize the surface recording density of about 100-200 gigabits/platter, it is desired to use a magnetic material having a high saturation magnetic flux density such as 2.3 T.
A high frequency performance of the induction type thin film magnetic head is also determined by a magnetic path length which is defined as a length from the throat height zero position to the back-gap. A high frequency performance of the thin film magnetic head is improved by shortening the above mentioned magnetic path length. It would be possible to shorten the magnetic path length by reducing a pitch of successive coil windings of the thin film coil, but this solution has a limitation. Then, there has been proposed to construct the thin film coil to have two coil layers as explained above. Upon forming the two-layer thin film coil, after forming a first thin film coil layer, an insulating film of photoresist is formed with a thickness of about 2 μm. This insulating layer has a round outer surface, and thus upon forming a second thin film coil layer, a seed layer for electrolytic plating has to be formed on an inclined portion. Therefore, when the seed layer is etched by the ion milling, a portion of the seed layer hidden by the inclined portion could not be removed sufficiently and coil windings might be short-circuited. Therefore, the second thin film coil has to be formed on a flat surface of the insulating layer.
For instance, it is now assumed that a thickness of the first thin film coil layer is 2-3 μm, a thickness of the insulating film formed on the first thin film coil layer is 2 μm, and an apex angle of the inclined portion of the insulating film is 45-55°, an outer surface of the second thin film coil layer must be separated from the throat height zero reference position by a distance of 6-8 μm which is twice a distance from the throat height zero reference position to the outer surface of the first thin film coil layer. Then, a magnetic path length would be longer accordingly. When the thin film coil has space/line of 0.4-0.5 μm/0.3-0.4 μm and a total number of coil windings is eleven, six coil windings are provided in the first thin film coil layer and five coil windings are formed in the second thin film coil layer. Then, a length of the whole thin film coil becomes 11.5 μm. In this manner, in the known thin film magnetic head, a magnetic path length could not be shortened, and a high frequency property could not be improved.
In the known combination type thin film magnetic head explained above, there is a problem of miniaturizing the writing inductive type thin film magnetic head element. That is to say, by reducing the magnetic path length LM, i.e. a length portions of the bottom pole 10 and top pole 21 surrounding the thin film coil 16, 19 as shown in FIG. 9, a flux rise time, non-linear transition shift NLTS and over write property of the inductive type thin film magnetic head element can be improved. In order to shorten the magnetic path length LM, a coil width LC of a portion of the thin film coil 16, 19 surrounded by the bottom pole 10 and the top pole 21 has to be shortened. In the known thin film magnetic head, the coil width LC could not be shortened due to the following reason.
In order to shorten the coil width LC in the known inductive type thin film magnetic head element, a width of coil windings of the thin film coil must be shortened, and at the same time, a distance between successive coil windings must be shortened. However, in order to reduce an electric resistance of the thin film coil, a width of coil winding could be shortened only with a limitation. When the thin film coil is made of copper having a high conductivity, a width of coil winding could not be reduced less than 0.3-0.4 μm, because a height of the thin film coil is limited to 2-3 μm. If a width of coil winding is shortened not larger than the above mentioned value, a property of the GMR film 15 might be deteriorated due to heat generated by the thin film coil. Furthermore, the bottom pole 10 and top pole 21 are also heated to expand and a serious problem of pole protrusion might occur and the thin film magnetic head might be brought into contact with the record medium. Therefore, in order to reduce the coil width LC without shortening a width of coil winding, a distance between successive coil windings must be shortened and a height of the coil has to be increased.
In the known thin film magnetic head, a distance between coil windings of the thin film coil 16, 19 could not be shortened. Now a reason of this will be explained. As explained above, the coil windings of the thin film coil are formed by the electrolytic plating method using the copper sulfate liquid. In order to deposit a copper film uniformly within the opening formed in the resist film formed on the seed layer, the seed layer is first formed with a thickness of 100 nm, and then the copper film deposited by the electrolytic plating on the seed layer through the opening formed in the resist film to form the coil windings. After that, the seed layer is selectively removed to separate the coil windings. The seed layer is removed by the ion beam milling using, for instance an argon gas, while the coil windings are used as a mask.
In order to remove the seed layer between successive coil windings, it is preferable to perform the ion beam milling from a direction perpendicular to the wafer surface. However, this result in a re-deposition of debris of the seed material and successive coil windings might not be separated well, and thus a distance between successive coil windings could not be shortened. Such a problem could be solved by effecting the ion beam milling at an angle of 5-10°, a sufficient ion irradiation could not be attained at a shadow portion of the photoresist film and the seed layer might be remained partially. Therefore, a distance between successive coil windings could not be shortened in order to prevent an insufficient insulation between coil windings. In the known thin film magnetic head, a distance between successive coil windings is long such as 0.3-0.4 μm. If a distance between successive coil windings is shortened less than the above value, the above mentioned problem might occur.
When the thin film coil 16, 19 is formed by the electrolytic plating method as explained above, in order to keep a thickness of the thin film coil uniformly, a plating liquid such as a copper sulfate must be stirred during the plating. If a width of a wall defining the opening in the photoresist film is shorted in order to shorten a distance between successive coil windings, the thin wall might be broken due to the stirring of the plating liquid. Then, the thin film coil could not be formed accurately. Also from this point of view, a distance between successive coil windings of the thin film coil could not be shortened.
The NLTS property of the inductive type thin film magnetic head could be improved by increasing the number of coil windings of the thin film coil. In order to increase the number of coil windings without increasing the magnetic path length, the number of thin film coil layers has to be increased to four or five layers. However, then an apex angle might be increased and a narrow track width could not be attained. In order to keep an apex angle within a given range, it is preferable to limit the number of thin film coil layers to not larger than three, preferably two. Then, the number of coil windings could not be increased and the NLTS property could not be improved.
Furthermore, when two thin film coil layers are provided as explained above, the second layer thin film coil 19 could not be formed perpendicularly, because the insulating film 17 is not flat, but is inclined at a peripheral portion of the second layer thin film coil. For instance, when a thin film coil having a space not larger than 0.3 μm with a thickness not less than 2.5 μm, argon ions could not effectively go onto the seed layer 18 between successive coil windings at a portion in which the thin film coil is not formed perpendicularly. Moreover, since an angle of the ion milling differs between a central portion and a peripheral portion of the wafer, the seed layer 18 could not be removed sufficiently and might be remained partially. When a space between successive coil windings is short, even if argon particles enter into this narrow space, Cu particles carried out together with argon particles might be deposited on side wall of the coil windings. Such etching debris might short-circuit the coil windings.
In Japanese Patent Application Laid-open Publication Kokai Sho 55-41012, there is disclosed a thin film coil, in which first and second thin film halves are arranged alternately with interposing therebetween an insulating film. In FIG. 7 of the Publication, there is shown a thin film coil, in which first and second thin film coils of a first layer thin film coil are formed as coils of anti-clockwise direction, and first and second thin film coil halves of a second layer thin film coil are formed as coil of a clockwise direction, and inner contact pads are connected to each other and outer contact pads are connected to each other such that an electric current flows in a same direction. However, in this known thin film coil, after forming the first thin film coil half, an insulating film and a conductive film are formed on a whole surface by sputtering or vacuum deposition, and a mask is formed selectively on the conductive film. After that, a portion of the conductive film formed above the first thin film coil half is selectively etched such that a portion of the conductive film deposited in a space between successive coil windings of the first thin film coil half is remained to form the second thin film coil half. Therefore, the first and second thin film coil halves are not formed in a self-aligned manner and a distance between successive coil windings could not be shortened in the order of submicrons.
One of the inventors of the present application has proposed in U.S. Pat. Nos. 6,191,916 and 6,204,997 a method of manufacturing a thin film coil, in which after forming a first thin film coil half by the electrolytic plating process using a seed layer, a thin insulating film and a seed layer are formed on a whole surface, a photoresist film having openings at portions corresponding to spaces of successive coil windings of the first thin film coil half is formed, and a second thin film coil half is formed by the electrolytic plating process using the photoresist film as a mask. In this method of manufacturing the thin film coil, the first and second thin film coil halves can be formed accurately by the electrolytic plating.
However, since use is made of the photoresist film having a given patter of openings for forming the second thin film coil half, the first and second thin film coil halves could not be formed in a self-aligned manner. Therefore, it is difficult to shorten a space between successive coil windings in the order of quartermicrons.